1. Field of the Invention
This invention relates to apparatus and methods for opening perforations in well casings, and more particularly, to a casing section having a plurality of holes plugged with ceramic rupture discs or inserts which can be ruptured by a mild explosive charge.
2. Description of the Prior Art
In the completion of oil and gas wells, it is a common practice to cement a casing string or liner in a wellbore and to perforate the casing string at a location adjacent to the oil or gas containing formation to open the formation into fluid communication with the inside of the casing string. To carry out this perforating procedure, numerous perforating devices have been developed which direct the explosive charge to penetrate the casing, the cement outside the casing and the formation.
In many instances in the completion and service of oil and gas wells, it is desirable to have a method and apparatus whereby perforations can be opened in the well casing string without penetrating the various layers of cement, resin-coated sand or other material located around the exterior of the casing string. Also, in some instances it is desirable to isolate sections of the well casing such that the sections do not have cement or other materials around the exterior of the isolated section. That is, there is cement above and below a casing section but not around it, which leaves an open annulus between the casing and the wellbore and associated formation. It may further be desirable to perforate such a section without the perforation penetrating the formation itself.
The present invention provides an apparatus and method for carrying out such procedures by utilizing a casing section which is plugged with ceramic discs or inserts which can be ruptured in response to an explosive charge detonated within the well casing and adjacent to the ceramic discs.